Field of the Invention
The present invention relates to an aqueous ink, an ink cartridge and an ink jet recording method.
Description of the Related Art
In recent years, it has been required to improve an optical density of an image upon printing a business document including characters and diagrams with an ink on a recording medium such as plain paper. It is advantageous from the viewpoint of the optical density of the image to use a self-dispersible pigment as a coloring material of the ink. The self-dispersible pigment is mainly produced by a chemical pigment-modifying technology, and an attempt to increase an introduced amount of a functional group is made.
For example, Japanese Patent Application Laid-Open No. 2000-512329, Japanese Patent Application Laid-Open No. 2003-535949 and Japanese Patent Application Laid-Open No. 2012-528917 describe a self-dispersible pigment to which a specified amount of a functional group has been bonded. In addition, Japanese Patent Application Laid-Open No. 2003-096350 describes an ink using a pigment that an average value of zeta potential and a polydisperse index falling within respective specified ranges. Further, Japanese Patent Application Laid-Open No. 2010-275478 describes an ink using a pigment treated with a specified azo compound subsequently to an oxidation treatment.
However, when the conventional self-dispersible pigments described in Japanese Patent Application Laid-Open No. 2000-512329, Japanese Patent Application Laid-Open No. 2003-535949, Japanese Patent Application Laid-Open No. 2012-528917, Japanese Patent Application Laid-Open No. 2003-096350 and Japanese Patent Application Laid-Open No. 2010-275478 are used, an image recorded has a high optical density as a measured value. However, uniformity of the image is poor, and the image is in a state unevenness like occurrence of white blur has occurred when visually observed.